Updated 2026-06-25
Carrier Furnace Code 33: What It Means & How to Fix It
Compiled & reviewed by Nikolai Tsyrenov · Updated 2026-06-25 · confidence: high
What does Carrier furnace code 33 mean?
Limit circuit fault — the high-limit or flame-rollout switch is open because the furnace is overheating, almost always from restricted airflow. Most often caused by The high-limit switch or flame-rollout switch is open due to overheating.
What Carrier furnace code 33 means
Limit circuit fault — the high-limit or flame-rollout switch is open because the furnace is overheating, almost always from restricted airflow.
Common causes
- The high-limit switch or flame-rollout switch is open due to overheating
- Restricted airflow from a dirty/clogged air filter (most common cause)
- Closed, blocked, or too few supply registers or return grilles, or restrictive ductwork
- A failing blower motor or wrong blower speed; if the switch stays open over 3 minutes the control escalates to lockout code 13
Homeowner-safe steps to try
- Turn the thermostat OFF and check/replace the air filter — a dirty filter is by far the most common cause
- Open all supply registers and make sure return-air grilles are unobstructed
- Remove furniture, rugs, or boxes blocking vents and returns
- Cycle power at the furnace switch after correcting airflow; do NOT press, jumper, or bypass any limit or rollout switch
When to call a licensed HVAC technician
If the basic checks below don't clear the code, the fault recurs, or anything involves the gas valve, burners, flame sensor or wiring, stop and book a licensed HVAC technician. Repairs to the combustion or gas system are not DIY.
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
When to call a pro: Call a licensed HVAC technician if code 33 returns after replacing the filter and opening vents, or if it escalates to code 13 — a repeatedly tripping limit can indicate a blower problem, restricted ducts, or a heat-exchanger/venting hazard. A tripped flame-rollout switch in particular needs professional inspection.
Carrier furnace code 33 FAQ
What does Carrier furnace code 33 mean?
Limit circuit fault — the high-limit or flame-rollout switch is open because the furnace is overheating, almost always from restricted airflow.
What causes Carrier furnace code 33?
Common causes: The high-limit switch or flame-rollout switch is open due to overheating; Restricted airflow from a dirty/clogged air filter (most common cause); Closed, blocked, or too few supply registers or return grilles, or restrictive ductwork; A failing blower motor or wrong blower speed; if the switch stays open over 3 minutes the control escalates to lockout code 13.
Can I fix Carrier furnace code 33 myself?
You can safely try: Turn the thermostat OFF and check/replace the air filter — a dirty filter is by far the most common cause; Open all supply registers and make sure return-air grilles are unobstructed; Remove furniture, rugs, or boxes blocking vents and returns; Cycle power at the furnace switch after correcting airflow; do NOT press, jumper, or bypass any limit or rollout switch. Call a licensed HVAC technician if code 33 returns after replacing the filter and opening vents, or if it escalates to code 13 — a repeatedly tripping limit can indicate a blower problem, restricted ducts, or a heat-exchanger/venting hazard. A tripped flame-rollout switch in particular needs professional inspection.
Other Carrier furnace codes
Carrier Code 11No previous code stored — the control has no fCarrier Code 12Blower on after power up — the blower runs forCarrier Code 13Limit circuit lockout — the lockout version ofCarrier Code 24Secondary-voltage fuse is open — the 3-amp conCarrier Code 25Model-selection or setup error — the control bCarrier Code 31Pressure switch or relay did not close, or reoCarrier Code 32Low-heat pressure switch did not close, or reoCarrier Code 34Ignition-proving fault — flame was not sensed,
Sources: shareddocs.com · manualslib.com. General information for homeowners, not professional advice — confirm against your furnace's manual and a licensed technician.